Nutrient Contents in Common Crop Residue

by Trenton Roberts, Associate Professor and Extension Soil Fertility Specialist - July 26, 2022

There have been several questions over the past few weeks regarding the nutrient content of crop residues commonly grown in the Arkansas delta and the possible overall value. With the persistent drought threatening to lower the productivity of pasture and hayland even further, more and more livestock producers are interested in crop residues as a potential hay/roughage source. This updated information is from an article posted in the fall of 2012. Just like Dr. Rick Norman said, “If you stay in this game long enough, everything cycles back around – even the fashion…”

Anyone who has grown rice or corn knows that there is plenty of straw and stubble out there following harvest, and with the recent drought, many people are looking to purchase hay/straw/stubble – anything they can get their hands on. In this situation, remember the statement “SELLER BEWARE!” The thought of making extra money from selling straw and stubble which is a hassle to roll down and work up is a very hard bargain to pass up, but few producers truly understand the value of the straw they are sending to the far corners of the earth. When I sat down to write this article I thought, “If I was a producer, what would I want to know about baling straw and stubble?” I would like to know what my straw and stubble are worth – what is the true value of all that mess? The best approach is to consider the amount and the value of the nutrients contained in the straw and stubble. The amount of plant essential nutrients contained in rice straw is easy to put a price tag on, especially with current potash prices near $880/ton.

How much are straw and stubble worth in terms of the nutrients it contains?

With the current drought, many people are looking for any type of forage or hay possible, and the thought of not having to deal will all of the stubble and straw following harvest is very appealing. The question of the day is, “how much are my straw and stubble worth in terms of the nutrients it contains?” My first approach was to tell producers what the value of the straw is on a per acre basis, but that approach is way too simplistic. A well maintained rice or corn crop can produce between 6,000 and 12,000 pounds of “straw or stubble,” but that doesn’t mean all of that biomass can be baled and removed following harvest. Cutting height, moisture, and whether or not you mow following harvest all play a role in determining the amount of stubble available to bale. Therefore, the best approach to use when selling straw or stubble should be to estimate the tonnage being removed and calculate the relative value of the straw. Most rice straw contains roughly 1% K and 0.125% P, which may not seem like a lot, but when you consider the amount of stubble that can be cut, baled and hauled off, it starts to add up real fast. On a per acre basis, it is safe to say that there will be 10,000 lb rice straw following harvest.

At the average values listed above, that relates to roughly 120 lbs of K₂O per acre and 25 lbs of P₂O₅ contained in 10,000 lbs of rice straw.
At current market prices for potash and phosphorous, that relates to about $115 of nutrients (potash and phosphorous) per acre that could be removed in 10,000 lbs of rice straw.

The next issue that complicates this discussion is the number of bales per acre, which is often how the producer is paid. If you remove the straw immediately following harvest, you will make a lot more bales per acre due to the increased weight of the straw than if you waited and let the straw dry before baling. A producer should focus on the tonnage of straw or stubble removed and the relative cost of nutrients on a tonnage basis to ensure that you are getting paid for the nutrients removed – not the number of bales. Few people consider the value of the straw that is rolled/tilled back into the soil following harvest, but when a producer sells straw, those are nutrients leaving the farm that will have to be replaced, most likely through purchasing fertilizer. When straw is rolled and tilled back into the soil following harvest, the majority of the nutrients contained in the straw will return to the soil and help to maintain soil nutrient levels. In fact, while the straw lies on the soil surface, potash can actually leach out of the straw and back into the soil, but when a producer sells straw, those are nutrients leaving the farm that will have to be replaced, most likely through purchasing fertilizer. To keep things fair and prevent producers from losing money, we have established the following guidelines to help aid producers when considering whether or not to sell straw and stubble following harvest.

Estimating Value of Straw and Stubble

Estimate the quantity of straw and stubble removed on a tonnage basis. To prevent "giving away” straw and stubble, try and calculate the tonnage of stubble actually removed, not the number of bales per acre. You can get in the ballpark by asking the buyer the weight of bales or calculating this yourself. The average rice and corn crops will produce between 6,000 and 12,000 lbs of stubble per acre. Peanuts and soybean produce somewhere in the neighborhood of 2,000 to 4,000 lbs of stubble.

Determine the quantity of nutrients removed. The following table provides some guidelines for phosphorous and potassium concentrations in common crop stubbles.

Crop Stubble	lbs K₂O per ton stubble	lbs P₂O₅ per ton of stubble
Rice	24	6
Corn	40	6
Grain Sorghum	42	8
Soybean	37	9
Peanut	41	7

Determine the “value” of nutrients removed. Once you have determined the quantity of nutrients removed, you can begin to place a value on those nutrients using the following data, which estimates that current cost of potash and phosphorous. At current market prices, potash is roughly $0.73 per lb K₂O ($880/ton potash), and phosphorous is $0.90 per lb P₂O₅ ($828/ton TSP). These values are for two nutrients and do not take into account the many other plant essential nutrients that are contained in crop stubble and are being removed with the P and K. Although nutrient value is important, many other intangibles cannot be easily measured such as the value of the organic matter returned to the soil in crop stubble or the potential habitat for feathered friends that we love so much in the Mid-south.

Example Calculation

(2,000 lbs of rice straw) x (24 lbs K₂O per ton) x ($0.73 per lb K2O) = $17.52 per ton

(2,000 lbs of rice straw) x (6 lbs P₂O₅ per ton) x ($0.90 per lb P₂O₅) = $5.40 per ton

$17.52 (value of K2O per ton of rice straw)
+ $ 5.40 (value of P2O5 per ton of rice straw)
$22.92 per ton of rice straw

Forage Analysis and Additional Considerations

If you are really interested in knowing the exact value of nutrients contained in your crop stubble several diagnostic labs can analyze that. Much like forage analysis, these reports can provide an exact nutrient concentration for each field, etc., and take out the “guesswork”. When sampling crop stubble, take 15-20 handfuls of straw randomly per field and chop or cut with scissors to roughly 6-inch sections and mix. After chopping and mixing, take a 1-gallon sealable plastic bag and fill it with a subsample. The University of Arkansas Agricultural Diagnostic Lab (1366 W. Altheimer Dr., Fayetteville, AR 72704) can perform the analysis for $18.00 per sample. Taking straw samples for analysis will give you a precise quantity of nutrients and ensure you are not “giving” nutrients away.

When selling straw or stubble, the best approach should be to consider the nutrient value removed on a tonnage basis and make sure you are compensated for the nutrients removed. Producers should let the buyers know up front that they would at least like compensation for the nutrients they are selling, and that way the producer can at least recover the cost of the nutrients they are selling and lowers the risk of getting left holding the bill. Another item to consider is the “unknown." The above quoted prices are current market prices for potash and phosphorous, but who’s to say that prices won’t go up? –especially with the uncertainty in the global markets right now.

Final Thoughts on Baling Straw and Stubble

Baling rice straw and selling it may seem like a very lucrative deal because it makes the ground easier to work up for soybeans. Plus, you may get a little money in your pocket. The analysis that we present here has attempted to put a price tag on the value of stubble based on the amount of potash and phosphorous contained in the straw and removed from the farm. Although the value of potash and phosphorous are very significant, there are many other factors to be considered which are much harder to put a price tag on. Rice stubble may seem like a hassle to mess with, but the organic matter that rice straw returns to the soil helps to improve soil structure, increases water holding capacity and returns a number of plant essential nutrients to the soil. Decisions are often based on immediate benefit/cost, with little foresight to the long-term impacts. When selling rice straw, remember that there is a significant value to that straw. Although it may seem beneficial in the short term, it may actually end up costing you money in the long term when your soil test reports start calling for 120 lbs of potash rather than 60.